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Genetic Analysis Using Genomic Representations Proc. Natl. Acad. Sci. USA Vol. 95, pp. 4487–4492, April 1998 Genetics Genetic analysis using genomic representations ROBERT LUCITO*, MARIKO NAKIMURA*, JOSEPH A. WEST*, YING HAN*, KOEI CHIN†,KENDALL JENSEN*, RICHARD MCCOMBIE*, JOE W. GRAY†, AND MICHAEL WIGLER*‡ *Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724; and †Department of Laboratory Medicine, University of California, San Francisco, Box 0808 MCB 230, San Francisco, CA 94143-0808 Contributed by Michael Wigler, February 3, 1998 ABSTRACT Analysis of the genetic changes in human RBgl-24 [as used in Lisitsyn et al. (1)], oligonucleotides used tumors is often problematical because of the presence of for PCR of World-Wide Web probes, and tetranucleotide normal stroma and the limited availability of pure tumor repeat D17S695 were synthesized by BioSynthesis (Lewisville, DNA. However, large amounts of highly reproducible ‘‘repre- TX). Genescreen Plus was purchased from DuPont. Radioac- sentations’’ of tumor and normal genomes can be made by tive nucleotides, rediprime labeling kit, dNTPs, and hyperfilm PCR from nanogram amounts of restriction endonuclease were purchased from Amersham Pharmacia Biotech (Uppsala, cleaved DNA that has been ligated to oligonucleotide adaptors. Sweden). Cell lines used were obtained through American We show here that representations are useful for many types Type Culture Collection, grown in culture, and DNA- of genetic analyses, including measuring relative gene copy prepared. Normal human placenta DNA was obtained from number, loss of heterozygosity, and comparative genomic CLONTECH. Oligonucleotides and probes for use with the hybridization. Representations may be prepared even from Applied Biosystems 7700 Sequence Detector were synthesized sorted nuclei from fixed and archived tumor biopsies. by Applied Biosystems. Nusieve agarose gels used for analysis of PCR products were purchased from FMC. World-Wide Analysis of the genetic changes in human tumors is often Web probe sequences were downloaded from the Massachu- problematical because of the presence of normal stroma. setts Institute of Technology human genome sequencing da- Although either microdissection or flow cytometry can pro- tabase (http:yywww-genome.wi.mit.eduy). duce small samples highly enriched for tumor cells or nuclei, Production of Representations. Genomic DNA (3–10 ng) the extracted DNA is of insufficient quantity for most uses. was digested by the desired restriction endonucleases (DpnII Nevertheless, we have successfully performed a complex pro- and BglII) under conditions suggested by the supplier. The tocol, representational difference analysis (RDA), on such digest was purified by phenol extraction and then precipitated small samples. RDA is a subtractive DNA hybridization tech- in the presence of 10 mg of tRNA. The digested DNA was nique that discovers the differences between paired normal resuspended by the addition of 444 pmol of each adaptor and tumor genomes (1). The first step of RDA is the prepa- (RBgl24 and RBgl12), T4 DNA ligase buffer (diluted to 13, ration of ‘‘representations,’’ which are highly reproducible provided with enzyme), and water to bring the volume to 30 ml. reformattings and amplifications of DNA populations. Typi- The reaction was placed in a 55°C heat block, and the cally, a representation is a set of restriction endonuclease temperature was decreased slowly to 15°C by placing the heat fragments of a limited size range amplified by PCR. As much ' m block at 4°C (for 1 hr). On reaching 15°C, the RBgl24 as 100 g of DNA can be prepared from as little as 3 ng of adaptor was ligated by the addition of 400 units of T4 DNA ' 3 3 DNA ( 1 10 cells). ligase and by incubation at 15°C for 12–18 hr. The ligated In RDA, a representation with much lower complexity than material was divided into two tubes, and the following was the starting population is needed to enable a subtractive added: 80 mlof53 PCR buffer [335 mM TriszHCl, pH 8.8y20 hybridization step to proceed effectively. Such low complexity y y b y mM MgCl2 80 mM (NH4)2SO4 50 mM -mercaptoethanol representations (LCRs) do not ‘‘capture’’ enough (typically, 9 9 # 0.5 mg/ml of BSA], 2 -deoxynucleoside 5 -triphosphates to a 7%) of the genome to be useful for many of the more final concentration of 0.32 mM, RBgl24 adaptor to a final common types of analyses. However, we demonstrate here that m concentration of 0.6 M, and H2O to bring the volume to 400 high complexity representations (HCRs) can provide ample ml. Each reaction was overlaid with 100 ml of mineral oil. The amounts of DNA in a sufficiently reproducible manner suit- reaction was placed in a thermal cycler preheated at 72°C, and able for most conventional studies. We demonstrate one type 15 units of AmpliTaq was added to the tubes. The thermal of HCR that captures '70% of the genome and illustrate its cycler was set to continue at 72°C for 5 min to allow for filling use for determining gene copy number, deletion mapping, loss in the 39 ends of the ligated molecules. This step was followed of heterozygosity (LOH), and comparative genomic hybrid- by 20 cycles lasting 1 min at 95°C and 3 min at 72°C, with an ization (CGH). HCRs may be a generally useful means of ‘‘immortalizing’’ and archiving DNA for later analysis from additional extension of 10 min at 72°C after the last cycle. The nonrenewable sources. PCR was divided into two tubes (now a total of four tubes), and the following reagents were added: 40 ml53 PCR buffer (as above), dNTP to a final concentration of 0.32 mM, RBgl24 MATERIALS AND METHODS adaptor to a final concentration of 0.6 mM, water to bring the m m Materials. Restriction endonucleases as well as T4 DNA volume to 400 l, and 100 l of mineral oil. The tubes then ligase, T4 DNA polymerase, and T4 polynucleotide kinase were amplified for an additional five cycles with extension were supplied by New England Biolabs. AmpliTaq was sup- according to the above conditions. The reactions were purified plied by Perkin–Elmer. Oligonucleotide adaptors RBgl-12 and by phenol-chloroform and then precipitated by the addition of The publication costs of this article were defrayed in part by page charge Abbreviations: HCR, high complexity representation; LCR, low com- plexity representation; RDA, representational difference analysis; CGH, payment. This article must therefore be hereby marked ‘‘advertisement’’ in comparative genomic hybridization; LOH, loss of heterozygosity. accordance with 18 U.S.C. §1734 solely to indicate this fact. ‡To whom reprint requests should be addressed at: Cold Spring © 1998 by The National Academy of Sciences 0027-8424y98y954487-6$2.00y0 Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY PNAS is available online at http:yywww.pnas.org. 11724. e-mail: [email protected]. 4487 Downloaded by guest on October 1, 2021 4488 Genetics: Lucito et al. Proc. Natl. Acad. Sci. USA 95 (1998) 1y10th the reaction volume of sodium acetate (3M pH 5.2) and CGH. CGH was performed according to standard proce- by the addition of one reaction volume of isopropanol. dure (9) by using HCR DNAs and genomic DNAs prepared PTEN Tumor Suppressor Lori Genomic Sequencing. Bac- from BT474 and MCF7 as target and normal female human terial artificial chromosome DNA was purified by detergent lymphocyte as the reference. The genomic and HCR DNA lysis and polyethylene glycol precipitation. DNA (5 mg) was samples were labeled by nick-translation with fluorescein sheared and then repaired by using T4 DNA polymerase. isothiocyanate–12-dUTP and Texas Red 5-dUTP to produce Fragments in the range of 1.5–2 kb were isolated by gel DNA fragments ranging in size between 500 and 2,000 bp. fractionation and inserted into M13 by ligation. Sequencing Quantitative PCR. Primer and probe sequences were pro- reactions were done by using dye primer chemistry that uses duced according to the Applied Biosystems software PRIMER energy transfer primers (2) and thermosequenase polymerase EXPRESS. These primers and probes were used in a PCR that (3). Reactions were run on an Applied Biosystems 377 se- was placed in the Applied Biosystems 7700 Sequence Detector quencer for 6- to 8-hr sequence runs for analysis. Base calling and amplified as described (10, 11). Samples used were HCRs was carried out by using the program PHRED (P. Green, produced from DNA derived from nuclei of sorted primary University of Washington). The collection of initial data was tumor biopsies. After the PCR, the data of fluorescence assembled into a contig by using the automated assembly corresponding to cycle number were downloaded from the program PHRAP (P. Green). The database generated was Applied Biosystems 7700 Sequence Detector to Microsoft converted to XGAP format and edited by using XGAP (4, 5). EXCEL and analyzed to give the graphs shown later. After completion of '6-fold coverage, the finishing process was carried out by using the program FINISH (G. Marth, RESULTS Genome Sequencing Center at Washington University) to fill gaps in the contig. The Basic Method. DNA from samples, usually paired tumor Southern Blotting. Normal DNA from a tumor cell line or cells or nuclei and normal cells or nuclei, were processed in representations derived from sorted nuclei were digested with parallel to prepare representations. DNA was cleaved with a either DpnII or BglII. Digested genomic DNA (5.0 mg), restriction endonuclease, such as DpnII or BglII, that is not digested HCR (5.0 mg) , or digested LCR (0.5 mg) was loaded blocked by 5-methylcytosine, and double-stranded, cohesive, on a 1.5% agarose gel. The gel was transferred to Genescreen adaptor oligonucleotides were ligated to the fragment ends. Plus after electrophoresis was completed. After transfer, the The adaptors were not phosphorylated and therefore could not blot was hybridized in GIBCO prehybridization solution at be self-ligated to form interfering dimers.
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